Evaluation method and evaluation system for impact force of laser irradiation during laser peening and laser peening method and laser peening system

Abstract

A method of evaluating impact force input to a workpiece member with a laser irradiated in laser peening processing is provided. This evaluation method includes a signal acquiring step, an input function calculating step, and an evaluating step. In the signal acquiring step, a detected waveform is acquired. The detected waveform is output during the laser peening processing by an AE sensor that detects an elastic wave generated in the workpiece member. In the input function calculating step, an input function I(t) by laser irradiation is calculated. In the evaluating step, impact force is evaluated using the input function I(t) by the laser irradiation.

The invention claimed is: 
     
       1. A laser peening method, comprising:
 generating a shock wave by an ablation with a laser in a liquid to obtain a first peening effect; 
 obtaining a shock wave due to collapse of the cavitation bubbles generated by a pressure change that occurs in the liquid to obtain a second peening effect; 
 a signal acquiring step of acquiring a detected waveform output during a laser peening processing by an AE sensor that detects an elastic wave generated in a workpiece member; 
 an input function calculating step of calculating an input function I(t) by laser irradiation using, when the detected waveform is represented as V(t), an input function by the laser irradiation is represented as I(t), a response function of the AE sensor is represented as S(t), a green function of the workpiece member is represented as G(t), and a convolutional integral is represented as *, a first relational expression
     V ( t )= S ( t )* G ( t )* I ( t ) 
 
 
       and on the basis of the response function S(t) of the AE sensor acquired in advance, the green function G(t) of the workpiece member acquired in advance, and the detected waveform V(t) acquired in the signal acquiring step; and
 an evaluating step of evaluating impact force using the input function I(t) by the laser irradiation. 
 
     
     
       2. The laser peening method according to  claim 1 , wherein, in the input function calculating step, the input function I(t) is calculated using at least an AE waveform including a first peak amplitude value, which is an amplitude value of a peak detected first in the detected waveform acquired in the signal acquiring step. 
     
     
       3. The laser peening method according to  claim 2 , wherein, in the input function calculating step, the input function I(t) is calculated using, in the detected waveform acquired in the signal acquiring step, a second detected waveform detected after a first detected waveform having an amplitude value attenuated from the first peak amplitude value set as a maximum. 
     
     
       4. The laser peening method according to  claim 3 , wherein the second detected waveform is detected after at least 100 μs from the detection of the first detected waveform. 
     
     
       5. The laser peening method according to  claim 1 , wherein
 the input function calculating step includes an estimating step of estimating or specifying a function representing attenuation of a peak amplitude value of the detected waveform acquired in the signal acquiring step, and 
 the input function I(t) by the laser irradiation is calculated using the function estimated or specified by the estimating step and the peak amplitude value. 
 
     
     
       6. The laser peening method according to  claim 1 , wherein the response function S(t) of the AE sensor and the green function G(t) of the workpiece member are acquired by calibration and a simulation performed using a finite element method. 
     
     
       7. The laser peening method according to  claim 6 , wherein the calibration is performed using data obtained by breaking a lead of a mechanical pencil. 
     
     
       8. The laser peening method according to  claim 6 , wherein, in the simulation performed using the finite element method, the green function G(t) of the workpiece member is obtained using data concerning a shape and a material of the workpiece member and simulative impact force. 
     
     
       9. The laser peening method according to  claim 6 , wherein, when a detected waveform for the purpose of calculation is represented as V test (t), an input function for the purpose of calculation by an AE source is represented as I test (t), and the convolutional integral is represented as *, the green function G(t) of the workpiece member is acquired by a simulation using a second relational expression:
     V   test ( t )= G ( t )* I   test ( t ). 
 
     
     
       10. The laser peening method according to  claim 9 , wherein
 a detected waveform V e (t) obtained by breaking a lead, the green function G(t) of which is known, is acquired using the AE sensor, 
 a detected waveform V cal (t) for the purpose of calculation is acquired using an input function I cal (t) in breaking the lead according to a third relational expression:
     V   cal ( t )= G ( t )* I   cal ( t ) 
 
 and 
 the response function S(t) of the AE sensor is calculated using a fourth relational expression:
     V   e ( t )= S ( t )* G ( t )* I   cal ( t ), 
 
 
       the third relational expression, and the green function G(t) obtained by the simulation. 
     
     
       11. A laser peening method, comprising:
 generating a shock wave by an ablation with a laser in a liquid to obtain a first peening effect; 
 obtaining a shock wave due to collapse of the cavitation bubbles generated by a pressure change that occurs in the liquid to obtain a second peening effect; 
 a signal acquiring step of acquiring a detected waveform output during a laser peening processing by an AE sensor that detects an elastic wave generated in a workpiece member; 
 an input function calculating step of calculating an input function I(t) by laser irradiation using, when the detected waveform is represented as V(t), an input function by the laser irradiation is represented as I(t), a response function of the AE sensor is represented as S(t), a green function of the workpiece member is represented as G(t), and a convolutional integral is represented as *, a first relational expression
     V ( t )= S ( t )* G ( t )* I ( t ) 
 
 
       and on the basis of the response function S(t) of the AE sensor acquired in advance, the green function G(t) of the workpiece member acquired in advance, and the detected waveform V(t) acquired in the signal acquiring step; and
 an evaluating step of evaluating impact force using the input function I(t) by the laser irradiation, 
 wherein the ablation is caused in the liquid in order to obtain a shock wave due to cavitation bubbles, the liquid is water, a vector of a shock wave due to the ablation is changed by water confining the shock wave due to the ablation, not allowing the shock wave due to the ablation to be dispersed to the outside, and a wavelength of the laser is 532 nm as a second harmonic of 1064 nm such that the laser is not attenuated in the water and the water does not cause ablation. 
 
     
     
       12. The laser peening method according to  claim 11 , wherein, in the input function calculating step, the input function I(t) is calculated using at least an AE waveform including a first peak amplitude value, which is an amplitude value of a peak detected first in the detected waveform acquired in the signal acquiring step. 
     
     
       13. The laser peening method according to  claim 12 , wherein, in the input function calculating step, the input function I(t) is calculated using, in the detected waveform acquired in the signal acquiring step, a second detected waveform detected after a first detected waveform having an amplitude value attenuated from the first peak amplitude value set as a maximum. 
     
     
       14. The laser peening method according to  claim 13 , wherein the second detected waveform is detected after at least 100 μs from the detection of the first detected waveform. 
     
     
       15. The laser peening method according to  claim 11 , wherein
 the input function calculating step includes an estimating step of estimating or specifying a function representing attenuation of a peak amplitude value of the detected waveform acquired in the signal acquiring step, and 
 the input function I(t) by the laser irradiation is calculated using the function estimated or specified by the estimating step and the peak amplitude value. 
 
     
     
       16. The laser peening method according to  claim 11 , wherein the response function S(t) of the AE sensor and the green function G(t) of the workpiece member are acquired by calibration and a simulation performed using a finite element method. 
     
     
       17. The laser peening method according to  claim 16 , wherein the calibration is performed using data obtained by breaking a lead of a mechanical pencil. 
     
     
       18. The laser peening method according to  claim 16 , wherein, in the simulation performed using the finite element method, the green function G(t) of the workpiece member is obtained using data concerning a shape and a material of the workpiece member and simulative impact force. 
     
     
       19. The laser peening method according to  claim 16 , wherein, when a detected waveform for the purpose of calculation is represented as V test (t), an input function for the purpose of calculation by an AE source is represented as I test (t), and the convolutional integral is represented as *, the green function G(t) of the workpiece member is acquired by a simulation using a second relational expression:
     V   test ( t )= G ( t )* I   test ( t ). 
 
     
     
       20. The laser peening method according to  claim 19 , wherein
 a detected waveform V e (t) obtained by breaking a lead, the green function G(t) of which is known, is acquired using the AE sensor, 
 a detected waveform V cal (t) for the purpose of calculation is acquired using an input function I cal (t) in breaking the lead according to a third relational expression:
     V   cal ( t )= G ( t )* I   cal ( t ) 
 
 and 
 the response function S(t) of the AE sensor is calculated using a fourth relational expression:
     V   e ( t )= S ( t )* G ( t )* I   cal ( t ), 
 
 
       the third relational expression, and the green function G(t) obtained by the simulation.